1. Field of the Disclosure
The present invention relates to a pressure actuated sensor which serves as a switching device, for example, for activating and/or shutting down or controlling mechanical doors, equipment or machinery.
2. Description of the Related Art
Pressure actuated switches are known in the art. Such switches are used for example as safety mats, sensitive door edges, and the like. Typically, such switches include two spaced apart conductors. When pressure is applied the conductors contact each other, thereby closing an electrical circuit. This switching action can be used to activate or, alternatively, deactivate machinery. For example, on mechanically operated doors, the doors commonly include a sensitive edge switch. Should the edge switch make contact with an object in its path (e.g. a person) while the door is closing the edge switch will send a signal to a control unit to reverse or stop the movement of the door. Such edge switches may commonly be found on garage doors, train doors, and the like.
For example, U.S. Pat. No. 5,072,079 to Miller discloses a sensing edge causing a closing door to open by actuating a device upon force being applied to the sensing edge. The sensing edge includes a first sheet of resiliently compressible material, a first sheet of electrically conductive material, a layer of non-conductive material, a second sheet of electrically conductive material, a second sheet of resiliently compressible material and an elongate inner core arranged in the recited order. The inner core has a predetermined elastic compressibility which is selected in accordance with the desired sensitivity of the sensing edge, such that the sensitivity of the sensing edge directly corresponds to the elastic compressibility of the inner core. The first and second sheets of flexible, electrically conductive material are spaced apart by the layer of non-conductive material and present opposed portions to each other through an opening in the layer of non-conductive material whereby upon the application of force to the sheath, the inner core compresses until its elastic compressibility is less than the elastic compressibility of said first and second layers of resiliently compressible material and said layer of non-conductive material, whereupon a portion of the first sheet of flexible, electrically conductive material deflects into the opening in the second layer of non-conductive material and into contact with a portion of the second sheet of flexible, electrically conductive material to thereby actuate the device.
Other edge switches are disclosed, for example, in U.S. Pat. Nos. 5,027,552; 5,023,411; 4,920,241; 4,908,483; 4,785,143; 4,349,710; 4,273,974; 4,051,336; and 3,315,050.
While prior known edge switches are useful for detecting the presence of an object in the path of a moving door, being fully on or completely off they do not discriminate between the signals resulting from contact of the edge switch with large objects, and spurious signals resulting from, for example, disparities in the interfacing surfaces of the switch caused by uneven extrusion.
A freely hanging drape sensor which can distinguish between weak and strong activation of the sensor is disclosed in U.S. Pat. No. 5,856,644 to Burgess, and which is incorporated by reference herein in its entirety. The drape sensor disclosed in U.S. Pat. No. 5,856,644 includes a piezoresistive cellular material and a standoff layer for providing an analog signal correlated with the strength of the activation force, as well as an on-off function. The drape sensor can be used in conjunction with moving objects, such as electrically operated doors to provide safety door edges. Alternatively, the drape sensor can be used as a freely hanging curtain to detect objects moving into contact therewith.
One problem which can occur with drape sensors is internal condensation of moisture. This problem can occur when the drape sensor is positioned between a hot, moist environment on one side and a cold environment on the other side. While the polymeric outer covering of the drape sensor is non-porous and relatively impervious to water in the liquid state, there is nevertheless the possibility of molecular diffusion of water vapor through the polymer cover and into the interior of the sensor. The water vapor can condense inside the drape sensor, thereby affecting its operation if a sufficient amount of water accumulates.
The prevention of water related inconsistencies of operation, as well as other improvements, are provided by the drape sensor described herein.
A pressure actuated switching device for free hanging from a support, i.e., a drape sensor, is provided herein. The pressure actuated switching device includes: (a) an outer electrically non-conductive cover having an exterior surface, an interior surface, and a bottom edge, wherein the cover includes a plurality of weep holes disposed along the bottom edge; (b) a first electrically conductive coating deposited on the interior surface of the cover sheet; (c) an interior sheet having at least a first surface with a second electrically conductive coating deposited thereon; and (d) an electrically non-conductive spacer disposed between the first electrically conductive coating and the second electrically conductive coating.
Also included is at least one sensitizing bracket for promoting a sensitive response to the application of lateral or bottom applied force. The drape sensor is responsive to actuation along its sides, as well as along the bottom edge. Moreover, the drape sensor functions in extreme conditions of moisture, and hot and cold ambient conditions.